Technical Field
The present invention relates to an optical element measuring technology. More particularly, the present invention relates to a method, computer recordable media, system, and apparatus for obtaining a plurality of measurement errors of the optical element.
Related Art
An optical element has to be measured to make sure its performance after being finished with manufacture. The optical element may have an error as compared to what has been designed previously, and this error is called manufacture. Further, since the optical element is held on a measurement instrument in a measurement task, gravity of the optical element itself, a holding position and state may also result in errors. In addition, a system measurement error may occur on the combination of the optical element and the measurement instrument.
Typically, the measurement instrument is an interferometer or a wavefront sensor. The mentioned optical element may involve a convex lens, a concave lens, plane a mirror, aspherical concave, an aspherical concave, and the like. The mentioned errors may result in various forms of aberration, including several orders of spherical aberration, astigmatism, coma, trefoil, tetrafoil, and pentafoil aberrations. Each of the aberrations of several orders is a Zernike coefficient, and all the Zernike coefficients add together to from a Zernike polynomial, which presents a measurement result of the optical element. Such Zernike coefficients are provided in the conventional interferometer or wavefront sensor, which also provides a wavefront picture corresponding to the various levels of Zernike coefficients. In addition, the interferometer or wavefront sensor also provides an interference picture.
The above errors have a larger effect on performance of the optical elements having a larger diameter or precision. In addition, the gravity error of the optical element has a different value when the optical element is used in space. Generally, the optical elements are apt to have an affected measurement result owing to the holding and supporting means in the measuring task, and this error associated with the holding and supporting of the optical element presents an additional error to the optical element although the optical element has been polished and corrected according to the measurement result. Therefore, it is apparently quite a need to have an absolute measurement technology for optical elements.
Hence, the prior art absolute measuring technology cannot effectively separate the deformities contributed from the holding and gravity of the optical element, i.e. the Zernike coefficients contributed from the same cannot be understood and thus separated. Further, the improved means for the inaccurate measurement is applied for the most part, only with consideration of the gravity factor. At this time, the optical element is rotated 360 degrees, the interferometer or wavefront sensor emits a light ray to project on the optical element, and a light picture of a reflected version of the projected light ray are acquired. Further, the measurement data, i.e. wavefront error data with respect to a plurality of angles among the 360 degrees are averaged, and the averaged data are taken as a final wavefront error data. The angles for sample data taking are 0 degree and 360 degrees, or 0 degree, 90 degrees, 360 degrees, and 270 degrees.
However, this measurement result obtained by the prior measurement technology might not have a desired precision, and the other factors resulting in the measurement errors still have to be separated so as to have a more precise measurement result, simultaneously the polish process for the optical element manufacture may have a more correct basis. Therefore, there is quite a need to set forth an improved absolute measuring technology for optical elements.
In addition, the prior optical element measuring technology involves a use of an octal-axis adjustment mechanism and a complicated apparatus alignment process therefor. Therefore, the prior optical element measuring technology still has a space to improve for simplification.